The present invention relates to an improvement of an electromagnetic pump used for, e.g., supplying fuel to a vehicle.
A demand has arisen for an electromagnetic pump used as a vehicle fuel supply pump, which has a simple structure and can perform a stable pump operation without requiring high working and assembly precision of each component. Conventional electromagnetic pumps of this type, however, have their own advantages and disadvantages. A pump which can satisfy all the above characteristics has not been realized yet.
Cylindrical and square type pumps are generaly known as the conventional electromagnetic pumps of this type. The cylindrical type pump is designed such that a sleeve member for housing a plunger is arranged in a cylindrical housing, suction and delivery chambers are formed at both the ends of the sleeve member, and an electric chamber in which an excitation coil, a transistor, a printed circuit board, and the like are arranged is formed in a central portion of the sleeve member. The square type pump is designed such that a sleeve member for housing a plunger is arranged in a square housing, which is formed by assembling housing members each having a substantially U-shaped sectional area, so as to extend therethrough, and an excitation coil and the like are housed in the housing. However, each of the electromagnetic pumps having these conventional structures has a complicated structure and a large number of components, thereby posing problems in terms of working and assembly. In addition, a serious problem is posed when a decrease in size, weight, and cost of the overall pump is attempted. Therefore, some countermeasures must be taken.
The present inventors, therefore, reviewed the overall conventional pump structures described above, and proposed a simple electromagnetic pump in Japanese Utility Model Laid Open No. 61-70581 and the like. According to this electromagnetic pump, an arrangement of each portion is simplified, the number of components is decreased, working and assembly of each portion can be facilitated, and reliability of the operation can be increased, while a decrease in size, weight, and cost of the overall pump can be realized. More specifically, this simple electromagnetic pump is designed such that a pump housing is constituted by a substantially cup-like housing body and a lid for sealing an opening end of the housing body, and a resin coil bobbin arranged around a sleeve member for housing a plunger and used for winding an excitation coil, a printed circuit board stacked on the outer surface of one flange at a predetermined distance and used for mounting various electronic parts including a transistor, and a holder and the like stacked outward therefrom at a predetermined distance are sequentially stacked and housed in the pump housing, while the stacked components are biased toward the lid side by a leaf spring inserted in a bottom side of the housing body, thereby canceling variations in size of these components in the housing and obtaining a stable assembly state.
According to the structure of the simple pump described above, however, problems are still posed in an assembly process wherein the components such as the holder, the printed circuit board, and the coil bobbin including the leaf spring are sequentially stacked and incorporated in the housing body from the bottom side, the opening end is sealed by the lid, and the lid and housing body are integrally formed by caulking or the like. Therefore it leaves much room for improvement. More specifically, the simple pump of their type, it is required that a sleeve member for housing a plunger, a pair of magnetic cylinders constituting a magnetic circuit, which are fitted in both end portions of the sleeve member and adapted to reciprocate the plunger, and a sealing ring and the like which are arranged between these magnetic cylinders or the outer end sides of these cylinders so as to seal fluid paths constituted by the sleeve member and the like are housed and arranged in the housing body in addition to the above-described components. In the conventional pump structures, the sleeve member and the like are sequentially incorporated in the housing, the coil bobbin and the like are then stacked and housed, and the lid is mounted and fixed on the housing by caulking. In this case, the laminated body of the coil bobbin and the like is assembled while the leaf spring is compressed. When the lid is mounted on the housing, the components are moved toward the lid side due to the reaction force of the leaf spring, and are stably arranged in the pump housing. Note that the sleeve member is in a state wherein it can be integrally moved with the inner wall of the coil bobbin due to the friction of the seal ring interposed between the magnetic cylinders. Therefore, the sleeve member is also moved toward the lid side upon movement of the coil bobbin and the like toward the lid side. If the sleeve member is moved in this manner, the seal ring, which is interposed in the bottom side of the housing body so as to seal the bottom side, may be slipped off from the end portion of the sleeve member, so that the seal ring protrudes into the sleeve member or a compression force for providing a seal in the axial direction cannot be ensured. As a result, problems such as degradation in a sealing function at this portion are posed.
Since such problems occur especially in the caulking process of the lid, a test and the like are difficult to perform. Furthermore, since a repair of that portion must be performed by disassembling the overall housing, a serious problem is posed also in terms of assembly. Therefore, some countermeasures must be taken to realize a stable pump performance in consideration of these problems.